Traffic signal control system



y 1933. T. P. PREIST 2,117,981

TRAFFIC SIGNAL comm SYSTEM Filed March 2, 1935 4 Sheets-Sheet l WIRES {0, II, l3, 14,!7, and/g connect with INVENTOR 7740mm H/L/P Pea/a7" I dpuzp d ,2 3m M A TTORNE Y3 May 17, 1938. 'r. P. PREIST 2,

\ TRAFFIC SIGNAL CONTROL SYSTEM Filed March 2, 1935 4 Sheets- Sheet 2 625m PHAsE E I r0 V/a f3 (see Fly-4. 615 f0 ZZZ INVENTOR 7710/14/15 PH/up p s/sr Gem/mouse (0/ F 12) 77mm N0. 2

T. P. PREIST TRAFFIC SIGNAL CONTROL SYSTEM Filed March 2, 1935 M46TER M46752 7714B? Na/ (0/ Fig. l]

May 17, 1938.

' IN VEIVTOR Trroms PHIL/P Pei/5r BY V g WM, ,(3 010m, A TTORNE x5 Patented May 17, 1938 Z91 2,117,981 TRAFFIC SIGNAL CGNTROL SYSTEM Thomas Philip Preist, Poulton, Wailasey, England, assignor, by mesne assignments, to Auto matic Telephone & Electric Company Limited, London, England Application March 2, 1935, Serial No. 9,623 In Great Britain March 8, 1934 7 Claims. (Cl. 177339) The present invention relates to traffic control show certain features of these figures more fully. signals for use at road crossings or the like and Fig. shows one example of a time space chart is more particularly concerned with a progressive for a progressive system of traffic control signaltype traflic control system by means of which a ling as an illustration of how the present inven- 5 number of controllers located at successive intertion may provide for a flow of trafiic through a sections on a main road may be regulated from a series of intersections. master timer in a certain phase relationship to The system comprises a master timer shown in each other so that if the average speed of the Fig. 1 which is arranged to extend pulses over traffic is known, it is possible to time the control three common conductors which connect with a 10 signals so as to ensure a substantially continuous number of local controllers for the purpose of 10 flow of trailic along the main road. The chief regulating their time periods in relation to each object of this invention is to provide an improved: other. It may be mentiOned that the common system of the above type adapted to be controlled return conductor GR is not absolutely essential by impulses extended over common wires and in but its use obviates any possible trouble due to which the local controllers employ step by step differences of ground potential. E'ach local conmechanism which is operated intermittently and. troller such as that shown in Fig. 2 employs step not continuously throughout the timing periods. by step mec a for Operating a am Shaft According to one feature in a trafiic control syswhich controls circuit chang COIItaCtS- t t tem the operation of the controller for producend of each sig a Cycle the master e is ing the signal changes at an intersection is adaptarranged to t a s a Synchronizing pulse Which 20 ed to be controlled by current impulses transserves to ensure that all the local controllers mitted from an external source which in accord- Shall be in co phase relationship in r ness ance with their spacing and duration control a for t Commencement 0 t 1'16Xt y t r y gas discharge tube-condenser timing circuit. pr v n in y i h r p n y wh h may According to another feature in a name c have arisen in the previous cycle from becoming 25 trol system employing a plurality of sets of sig- C ulative. nals located at adjacent intersections the indih ys i assumed to be arranged f r opvidua-l controllers for producing the signal oration from A. C. mains and suitable rectifying changes at the different intersections are ararrangements Provided at the ast r t mer ranged to be controlled by impulses t ns itt d and the local controllers for obtaining direct cur- 30 continuously from a master tim r, th effect of rent to operate the discharge tube timing circuits. an impulse difiering at the individual controllers. The rectifying arrangements for t e aster timer A further feature is that in a traffic control are Shown in 1 and comprise a e mionic system employing a plurality of sets of signals Valve rectifier VLV and a transformer XFR p located at adjacent intersections the individual Vid'ed With Suitable p g D he live main 5 controllers for producing the signal changes at of the Cl Supply is connected to the pp p the various intersections include rotary step by ate tapping point of the pr m ry win in in acstep switches which are advanced by t a cordance with the electrical voltage available and pulses from a master timer and are arranged t the grounded main is connected to the left-hand 40 take up a position from which they can only be end of the il- III the form Shown t ree 40 advanced by a distinctive synchronizing impulse secondary windings are provided of which only transmitted to all the individual controllers 51- two a used. d these connect ely with multaneously from the master timer. The rotary the filament and electrodes of the rectifying valve stepping mechanism of the local controller may VLV Whith pp direct rent t0 the termibe of the type in which a solenoid switching dedesignated p v in a rectangle at a p en- 45 vice steps a cam-shaft through a series of positial which may Conveniently be of the Order Of tions in which cam contacts operate control cir- 400 volts. cuits. Considering now the operation of the master The invention will be better understood from timer, when the mains are connected up, a, cirthe following description of one method of carcult is completed for charging the condenser QA '50 rying it into effect taken in conjunction with the which extends as follows: positive terminal, Fig. accompanying drawings comprising Figs. 1 and 2 1, conductors Ill and H (which are normally conwhich when arranged side by side in consecutive nected together by the contacts of a change over order form a complete circuit, and also Figs. 3 switch in a reserve master timer as hereinafter 5 and 4 supplementing Figs. 1 and 2 respectively to described), armature wt, tenths of seconds adjusting switch TNT the contacts of which as shown connect with appropriate tapping points on the common resistance XB, common resistance XA which connects with the seconds adjusting switch SEC, conductor l2, to one side of the condenser QA, the other side being connected to the common grounded terminal shown as minus in a circle or a rectangle. The common resistance XB may be built up for instance of a plurality of 20,000 ohm resistances, the common resistance XA, of a plurality of 200,000 ohm resistances, and the capacity of the condenser QA may be 5 mi. After a suitable interval of time has elapsed as determined by the setting of the adjusting switches, the potential on the condenser QA will rise to the striking voltage of the gas discharge tube FA which thereupon flashes and operates relay A. Relay A at armature al, Fig. 1, completes a circuit for relay U which operates and completes a parallel circuit for relay V which thereupon operates also and locks up over its armature Di. Relay V, at armature v2 and its associated make-break device, Fig. 1, momentarily shunts the condenser QA by way of a low resistance to reduce the potential across its plates to zero. Relay A therefore releases, and is followed by relay U which then at armature u2 completes a circuit for operating relay W. Relay W at armature wl, Fig. 1,.connects line potential to the pulse lead PL extending to the local controllers, at armature w2 prepares a circuit for relay X, at armature w t alters the charging circuit for condenser QA so that it includes only the resistance YC, and at armature w5 completes a charging circuit for the condenser QB which functions later to control the generation of the synchronizing pulse. Condenser QA again commences to charge, this time by way of the resistance YC which may be, for example, of a value suitable for producing a charging period of one second, and after this has elapsed the gas discharge tube FA again strikes and operates relay A. Relay A is now effective in energizing relay X which in turn energizes relay Y. Relay Y locks independently of its original energizing circuit, through yl, and at armature g2 momentarily shunts the condenser QA to dissipate the charge. Relay A therefore releases and in turn releases relay X and when armature x2 engages its back contact relay Z operates. Relay Z at armature 2! brings about the release in turn of relays V, W and Y, and at armature 22, Fig. 1, momentarily completes a circuit between the conductors l3 and M extending to a reserve master timer, the function of which will be described later. Since the release of relay Y releases relay Z and therefore all relays are now in their normal position, the sequence of operations described will again be initiated and will be repeated to effect the intermittent application of pulses to the conductor PL as long as the conditions remain unchanged. It will be appreciated from the operations so far described that the master timer is adapted to generate pulses of one second duration andthat the interval between successive pulses may be varied by means of the adjusting switches SEC and TNT.

During the application of pulses to the PL lead, corresponding pulses are delivered by means of armature to condenser QB which is thus gradually charged through the high resistance YE and when the number of pulses corresponding to one complete signalling cycle has been received, the potential across the condenser QB will have risen somewhat above the striking voltage of the gas discharge tube FB. Accordingly, when relay V releases at the end of the last control pulse in the cycle, the tube FB will flash and energize relay B. Relay B at armature bl in turn energizes relay SY' which locks up and at armature syZ momentarily shunts condenser QB by way of the low resistance YB, and at armature 31/3 connects the live main to the synchronizing conductor SY for the purpose of transmitting a synchronizing pulse to all the local controllers to ensure that they shall be in phase in readiness for the commencement of the next cycle. The duration of the synchronizing pulse is measured by the same timing means as controls the gaps between control pulses and accordingly when relay V again operates at the commencement of the next control pulse, relay SY' releases and disconnects potential from the lead SY.

It may be pointed out that the functions of the relays U to Z could be carried out by a smaller number of relays if these were of the so-called two-step type but that owing to the use of alternating current for energizing purposes such an arrangement might be open to objection on the ground of unreliability.

In order to ensure reliable and uninterrupted service, a reserve master timer may be provided and arrangements made for suppressing the operation of such reserve master timer No. 2 while the normal master timer No. l is functioning satisfactorily.

One example of an arrangement of this character is shown in Fig. 3 which supplements Fig. 1. It will be understood that master timer No. 2 is similar to timer No. 1 except for the addition of a change-over switching relay CH and an armature at! on its relay A to operate relay CH. On account of this similarity only those parts of master timer No. 2 associated with the interlinking arrangement are shown in Fig. 3, these parts appearing in a rectangle with the parts legended to correspond with those of timer No. 1 in Fig. l, and with the wires for connection to master timer .No. 1 shown projecting from the rectangle and numbered to correspond with the k connectingrwires of timer No. 1 in Fig. 1. Associated with relay OH is a lock-up circuit over its armature c712 and contacts of a releasing key or switch K.

Change-over switch contacts c'hl associated with the conductors Ill and II for master timer No. 2 corresponding to conductors l0 and H for timer No. 1 are normally open thereby introducing the additional resistance YQ, similar to YD in the No. 1 timer, and which may be of the order of one megohm, into the charging circuit which considerably increases the normal time period. At the same time while master timer .No. 1 is functioning satisfactorily the armature 22 therein will repeatedly shunt the condenser QA of master timer No. 2 over the conductors l3 and 14 thereby preventing the timing circuit from becoming effective to operate the change-over relay CH. It

will be understood that conductors l3 and M of Fig. I extend to condenser QA of master timer No. 2 in Fig. 3 and the corresponding conductors I? and i8 connected with condenser QA of master timer No. '1 extend to contacts 22 on relay Z in master timer No. 2.

If however, a fault arises on timer No. l which I No. 1 will slowly rise to the striking value of its associated discharge tube which will thereupon flash and operate the relay corresponding to relay A. This in turn will operatethe change-over relay CH. A changeover to the master timer No. 2 is effected and this timer then takes over control of the system. The resistance YQ in the No.

2 machine is short circuited by armature chl and simultaneously resistance YD is introduced by armature 0723 into the charging circuit of master timer No. 1. Timer No. 2 now operates to the exclusion of the No. 1 machine. If desired the changeover may be arranged to operate an alarm.

Each of the local controllers, any one of which is illustrated in Fig. 2, may be comprised essentially of a battery of cams mounted on a common shaft and arranged to close contact springs in a certain order under control of a timing device in cooperation with the master timer of Fig. 1. The camshaft is rotated step by step under the control of a solenoid S which is impulsed at predetermined time periods from a gas discharge tube-condenser timing device. The cam assembly may consist of a standard unit, for use in a number of different circumstances, having 22 pairs of cam-operated contact springs, with six different cam positions. In the embodiment shown, the full number of contacts is not used, and the positions of the several cam contact pairs during each of the six positions of the camshaft are designated in the chart accompanying Figure 2.

Operation of certain of the cams controls the indications of the right of way signal; others, as will hereinafter appear, admit varying portions of the several resistances in the condenser charging circuit of the timing apparatus.

Before the circuit operations of the local controllers shown in Fig. 2 are described, it should be explained that this controller includes arrangements whereby it may be readily adapted with very slight alteration to function either as an isolated controller or as a local controller in a co-ordinated system. For this purpose certain of the key points in the circuit are brought out to terminals designated in the drawings by the letter Z followed by a number, which can be connected together in suitable combinations to obtain the desired operation.

If the controller is to operate as a self-contained unit terminals Zl and Z2 are connected by closing the switch between them and closing the switches connecting terminal Z'l to terminals Z8 and Z9. All dial readings of the adjusting switches will then be in seconds and the length of each signal interval may be read directly. In this case of course there will be no external connections over leads PL and SY.

If the controller is to be used as a local controller in a co-ordinated system the connections will differ according as the synchronizing pulse becomes effective in phase A or phase B. If the synchronizing pulse is to function in phase A, switches are closed only from Z5 to Z4, Z8 to Z1 and Zll to Zlll, while, if the synchronizing pulse is to function in phase B, they are closed only to connect Z5 to Z6, Z8 to Z9 and Zll to Zl2. In this case the amber dial readings only will be in seconds but the green dial readings will indicate the number of master timer pulses and must be read in conjunction with the time-distance chart of the system to determine the exact period.

In the circuit description which follows it will be considered that the controller shown in Fig. 2 is functioning as a local controller arranged to synchronize during phase A and accordingly the appropriate connecting switches have been shown closed across the proper Z points in the drawings. The current supply arrangements as shown in Fig. 2 are similar to those provided for the master timer and further description is therefore unnecessary. The various interval adjusting switches GA, AA, AB and GB, Fig. 2, corresponding to the green and amber settings of the two phases are wired to appropriate tapping points XAI to XAID and XBtI to XB9 of the two common resistances. The banks of the switches GA and GB may be graduated in one second steps, for example, and the banks connected to them through cams C2 and C13 graduated in 10 second steps, and, except where otherwise stated, the time intervals may be read off directly from the setting of these switches. In this instance the common resistances are built up of r 200,000 ohm units and two megohm units respectively.

It will now be assumed that the cam shaft is standing in position 3 giving the right of way to phase B. This may be confirmed from the table in Fig. 2 which shows the condition of the cams in each of the six positions of the shaft, a black circle or bar indicating those contacts which are closed. Since it has been assumed that the controller is functioning in a coordinated system, the relay P will be impulsed continuously over the common leads PL and CR under the control of the master timer. Accordingly at armature pl these pulses are repeated to the condenser QL over a circuit which may be traced from the positive terminal, which may be at a potential of approximately 400 volts, over adjusting switch GB, cam contacts Cl3 and common resistances in series, switch between terminals Z5 and Z4, cam contacts C4, armature pl to one side of the condenser QL, the other side being connected to ground. The pulses are therefore integrated by condenser QL and when a full complement have been received, the potential across its plates will rise to the striking value of the discharge tub-e FL which thereupon flashes and operates relay L. Relay L at armature Ll energizes the solenoid S which advances the cam shaft into position 4 and at springs SI shunts the condenser QL by way of a low resistance YL to dissipate the charge. In position 4 the green signals of phase B are extinguished, the amber signals of both phases are lighted (with switch AS closed) and the red signals of phase A are maintained. A charging circuit for the condenser QL is now completed over the amber switch AB and cam contacts Cl2, and as the cam contacts C6 arealso closed the charging of condenser QL proceeds continuously and the impulsing of relay P is without effect. When the full amber period has been timed, the discharge tube FL will again flash and the cam shaft will be stepped into position 5. In this position the amber signals are extinguished, the green signals are lighted to phase A and the red signals are lighted to phase B.

Since synchronization is to take place in this phase all timing circuits are now disconnected and the controller waits for the reception of the synchronizing pulse over the common conductor SY. When the synchronizing pulse is received, relay C operates and at armature cl energizes the solenoid to advance the cam shaft into position 6.

No change is made to the signals in position 6 but pulses for charging the condenser QL are now extended over the adjusting switch GA from positive D. C. via cam contact C2 and associated adjusting switch and common resistance, via switch from Z5 to Z4, cam contact C4, and pulsing relay contact pl to condenser QA. It will be understood that the switch GA has a somewhat different function to perform from that of the switch GB, in that it does not control the whole of the green period of phase A but is set to measure off that portion of the green period which must expire after the instant of synchronization so as to ensure that the controller bears its proper phase relationship to the remainder of the system. This period of time from the instant of synchronization to the end of the A green period in the individual controller represents the time spacing, or time ofiset, of that controller from the common synchronization time, the relative values of time offset in the different individual controllers determining the time phase relation of their transfer of right of way. The

setting for this time offset can be readily ascertained from the time and distance chart of the system and will ordinarily be different in each controller and as previously suggested in the case of some of the controllers it will occur in the B phase.

One example of a time-distance chart of a progressive system is shown in Fig. 5. The abscissae in this chart represent time and the ordinates represent distance. It is assumed that a series of intersections 9th to 15th Streets along a common street called Grand Avenue are provided with traffic signals and controllers for operating such signals cyclically in predetermined time relation, and the pattern of signal changes is indicated on the chart. The system illustrated in the chart provides for flow of traflic at a speed of about 2'? miles an hour along Grand Avenue progressively through the several intersections in both directions, and the two shaded diagonal bands show how traffic can move through the several intersections at the progressive speed without stopping. The small black bars which are repeated along the horizontal lines at each intersection represent the red signal period for Grand Avenue at that intersection and the open spaces represent the green signal period for Grand Avenue, the change signal periods being neglected for the purpose of simplicity. The offset of the end of the Grand Avenue green period from the common reference line or zero offset line as it is often called, is shown at two or three of the intersections for example. It will be noted for instance, that 15th Street has a zero offset and 11th Street has about a second offset.

Assuming Grand Avenue in the chart in Fig. 5 to be phase A of the controller of Fig. 2 at 11th Street for instance, the open space between the Zero offset line and the first bar to the left of it is the initial A green period and in the present instance is controlled by the synchronizing pulse terminated at the zero offset line and the open space to the right of the zero oiiset line, that is the offset, is timed by the local condenser time under control of adjusting switch GA. When the time oifset period in question has elapsed, tube or lamp FL will again flash and the cam shaft will he stepped into position I where the amber signals are lighted to both phases and the green signal to phase A is extinguished. The charging circuit for the condenser QL is now completed over the switch AA and after the required period has elapsed the tube FL will again flash to advance the cam shaft into position 2 where the amber signals are extinguished, the greensignal is lighted to phase B and the red signal is lighted to phase A. A quick step circuit is now completed by way of a low resistance YJ and cam contacts C3 for charging the condenser QL and almost immediately the tube FL again flashes to advance the cam shaft into position 3. No change is made to the signals in this position but the controller again comes under the influence of the master timer pulses and the cycle of operations continues as already described.

In order to provide a means for switching the controller out of service in case it should develop a fault, a second timing circuit is provided, comprising the condenser QM, discharge tube FM and relay M. This timing circuit is connected to the positive terminal by way of the comparatively high resistance YK which, for example, is of the order of 12 megohms. This provides a long timing period, so that in the ordinary course of events the circuit is prevented from becoming effective owing to the repeated short circuiting of condenser QM by the solenoid springs S2. If however, the controller develops a fault and the solenoid ceases to step, the potential on the condenser QM will eventually rise to the striking voltage of the tube FM which thereupon flashes and operates relay M. Relay M at armature ml completes a circuit over conductors l5 and i6 for operating a relay T, shown in Fig. 4, and which looks up to the mains over armature TI and the contacts of a key KL and at other armatures t2 and t3 operates an alarm BL and disconnects the main current supply from the controller respectively. All signals are therefore extinguished, and this condition obtains until the fault is cleared, whereupon the reoperation of the key releases the relay T and the mains are again reconnected.

As regards the timing circuits in general, it might be convenient in practice to make use of discharge tubes having appreciably different striking voltages, and in this case it would prob ably be desirable to provide adjusting means for compensating for these differences to ensure that the timing periods were not adversely affected thereby. This could be achieved by means of a potentiometer arrangement which would enable the tubes to be normally primed to a voltage equal to the amount by which they diifered from the standard chosen. For example, if the standard is set at 260 volts and a particular tube flashes at 250 volts, it will be necessary to prime this tube 10 volts negative to' secure correct timing. On the other hand a tube having a striking voltage of 270 would have to be primed 10 Volts positive to achieve the same results.

It will be observed that each of the local controllers in the embodiment of the invention above described includes a condenser timing device which in certain positions of the local control cycle cooperates with the master timer and in other positions as for example, the amber signal position, operates independently of the master timer. This local timing device operates similarly independently in one initial green position, while in the other initial green position it is disconnected, so that advancing of the switching mechanism from this position is normally accomplished only by direct operation of the solenoid of the mechanism by the master timer. In the second green signal position, even where the timing action is under the control of the spaced impulses over circuit PL of the master timer the condenser timing device of the local controller is still operating as a timer device during each such impulse. It will be appreciated that the condenser timing device does not reset to zero time after each PL impulse but is simply operated and suspended alternately so that its timing action proceeds progressively and, after a predetermined number of unit impulses, is completed. The total time period of such second green position is the result of the charge time rate of the condenser, or conversely the time setting of the condenser timing device and the time length of the master timer impulses.

The effect and significance of this can be seen if an example of a traflic control progressive system is assumed for purpose of illustration. Assume for instance, a master timer supervising local controllers at 12th and lath Streets in the chart of Figure 5. Under certain conditions an over-all cycle of 50 seconds'might be employed, as illustrated in the chart, the master timer operating on this cycle and the local controllers reaching their resynchronizing positions in-say 48 seconds, for example, but being resynchronized by the master to operate in a total cycle of 50 seconds. Including the short resynchronization period and considering a 50 second cycle of the local controllers, assume the controller at 12th Street is 30 seconds main street green, 3 seconds amber, 14 seconds cross street green, and three seconds amber. Assume also that the controller at 14th Street is 22 seconds main street green, 3 seconds amber, 22 seconds cross street green and 3 seconds amber. Now if the PL circuit impulses, supplied in common by the master timer to the two intersections, are assumed as one second long and one second apart, the condenser timing device at the 12th Street controller may be set at 15 unit impulses, or 15 seconds of cumulative impulse time for the main street green (neglecting the initial green for this example). At the 14th Street controller the corresponding timing device will be set at 11 impulses, or 11 seconds of charging time for the main street. At both 12th and 14th Streets the condenser timing device will be set for 3 seconds amber periods. For cross street green at 12th Street the setting is '7 and at 14th Street is 11. Now on each impulse during the main street green period the condenser at 12th Street is charged about 11/ 15s as far as the condenser at 14th Street, but in successive impulses either one condenser is charged about the same amount as that one condenser was in preceding impulses, or in other words is charged a substantially uniform proportion of the total cycle of its controller. denser timer on the lower and relatively straight portion of the well-known condenser charging time curve.

Suppose now that it is desired to change the over-all cycle of the system to 100 seconds to care for slower traffic for example at about 12 miles per hour. The master timer is then set to resynchronize the local controllers on a 100 second cycle and the spacing of the unit impulses is adjusted to about 3 seconds at the master timer, so that the total period of off and on for each impulse is 4 seconds or twice the former two seconds. Now, due to the increased spacing of the impulses, the main street green at 12th Street is automatically increased to about seconds and the main street green at 14th Street is increased to about 44 seconds without change of setting of the condenser timing device in either of the controllers at 12th and 14th Streets.

The cross street green is automatically increased at 12th Street proportionately to about 23 seconds and the cross street green at 14th Street is increased proportionately to 4% seconds. Due to the independence of the local timing de- This assumes operation of the con-' vice in the amber periods, these periods all remain the same at 3 seconds. The additional 6 seconds to make up the total of 100 may be absorbed in the resynchronization setting and adding that much green time to the street where the resynchronization occurs, for example.

Essentially, therefore, by means of the present invention the master timer can adjust the cycle of the local controllers substantially without disturbing the proportions of the cycle allocated to the main and cross streets at individual intersections. It will be appreciated that by using a condenser timing device operated by spaced impulses the movement of mechanical parts is minimized at the local controller, the only movement on individual PL impulses being that of a relay which can readily be designed for long life in such operation. The use of such timing device further provides readily for independent timing of amber signal periods to keep them constant, irrespective of change in total cycle.

Thus the object of the invention as brought out above and many others are achieved. It is to be understood that various modifications in the structural details or arrangements of the parts, or changes in the design herein exemplified may be made without departing from the spirit of the invention as defined by the claims.

The term timing device as used herein designates generally a device for performing one operation a definite time after another operation, and more particularly in this embodiment designates an electric condenser type timer adapted to be operated either steadily to actuate a control circuit after a time interval, or intermittently to alternately suspend and resume its timing action so as to actuate such control circuit after a cumulative operating period equal to such time interval.

The term timer is used herein for a mechanism including a timing device to generate impulses or operate control circuits periodically.

The term controller is used herein broadly to designate a mechanism for operating trafiic signals through a cycle of right of way indications to the respective lanes at an intersection of traffic lanes. Where this term is used with right of way, as right of way controller it includes appropriate right of way signals.

The terms local controller and individual controller emphasize the use of a controller at an individual intersection with supervision of its time cycle by an external timer termed a master timer, which latter is ordinarily remotely located and supervises other local controllers at other intersections for coordinated traiilc signalling the several intersections. In this embodiment such supervision preferably takes the form of synchronization of local controllers at least once per cycle, and also during a portion of each cycle, takes the form of alternate operation and suspension of operation of a timing device in the local controller in accordance with spaced impulses sent out from the master timer to maintain the length of such portion of the local controller cycle in proportion to the total cycle as determined by resynchronization.

Having described my invention what I claim as new and desire to secure by Letters Patent of the United States is:

1. In a traffic signal control system for a plurality of intersections of cross trafiic lanes with a common main lane, the combination of a right of way controller at each intersection for cyclically according and interrupting right of way on the intersecting lanes and each of said controllers including a cyclic step by step mechanism, and a device for advancing said cyclic mechanism through its cycle one step at a time, said device comprising a condenser, means operable responsive to a predetermined charge on said condenser to advance said mechanism one step and means when connected to said condenser for charging same, a master timer connected to each of said right of way controllers for transmitting to the controllers electrical impulses having certain time length and spacing, and impulse responsive means in each controller for connecting the charging means to the timing condenser thereat for the length of each spaced impulse during certain of said steps, and other means in said controller for charging the same said condenser in other of said steps in said cycle.

2. In a traffic signal control system for a plurality of intersections of cross traffic lanes with a common main lane having a right of way indicating means at each intersection and a controller thereat for operating the indicating means for cyclically according and interrupting right of way on the intersecting lanes, said controller including a cyclic step by step mechanism adapted to be advanced step by step and having means to change signal indications in stepping from one step to the next and a timer for timing when operable the advance of said cyclic mechanism from one step to the next, said timer comprised of a condenser, means when connected to said condenser for varying the charge from an initial value to a predetermined value, and means responsive to a predetermined value of charge on said condenser for stepping ahead said cyclic mechanism, a periodic impulse generating means at a central station for generating spaced electric impulses, a circuit from said generating means and common to all the controllers for transmitting said impulses from said generating means to said controllers, and means in each controller responsive to said impulses for connecting said charge varying means to said condenser for the duration of each of said impulses in at least one of said steps for rendering said timer operable for advancing the timing of each of said controllers substantially a uniform proportion of its cycle in successive impulses in said one step, and other means in each controller connected continuously to the same said condenser in another of the steps in said cycle to vary the charge on said condenser to said predetermined value in the latter step.

3. In a traffic control system for a plurality of intersections of traffic lanes, the combination or" right of way indicating means at each intersection, a controller therefor at each intersection including a rotary step-by-step mechanism adapted to be operated cyclically to operate said indicating means to accord right of way successively to each of said lanes at its intersection, and a timing device for advancing said mechanism at time intervals one step at a time through such cycle of right of way indications, said timing device comprising a condenser, and means connected to said condenser and operable responsive to a predetermined charge on said condenser to so advance said mechanism from one step to the next, means for charging said condenser when connected to the same, and master timer means in said system for periodically and simultaneously at the several intersections connecting and disconnecting alternately the respective said charging means to and from the respective said condensers during at least one of said time intervals and at time periods relatively short as compared with said one time interval to control the total length of said one time interval of said timing device, and other means in said controller continuously connected to the same said condenser in at least one other step in said cycle to charge said condenser to said predetermined value, whereby said controller will operate through such cycle.

4. In a signalling system having signalling circuits, step-by-step switching mechanism for operating said signalling circuits, a condenser adapted to be charged over a time period, means operating responsive to a predetermined charge ,on said condenser to advance said mechanism from one step to another, remote control means for said mechanism including a circuit transmitting periodic impulses of adjustable time length and adjustable time spacing, and means associated with said mechanism for charging said condenser at an adjustable time rate during said impulses in one of the steps.

5. In a traffic control system for a plurality of intersections of cross trailic lanes with a common main lane having right of way indicating means in each intersection for according and interrupting right of way on the intersecting lanes, the combination of a cyclic step by step mechanism having means to change the right of way signal indication from one lane to another in stepping from one step to the next, a condenser, means when connected to said condenser for varying a charge on said condenser from'an initial value to a different certain value, and means responsive to a said certain value of charge on said condenser for advancing said cyclic mechanism from step to step through such cycle and resetting the charge on said condenser to such initial charge on each such advance, a periodic i impulse generating means at a central station for generating spaced electric impulses, a circuit from said generating means and common to all of said condenser charge varying means at all said intersections for transmitting such impulses from said generating means to all said charge varying means, and means at each intersection responsive to said impulses to connect said charge varying means to said condenser during said impulses in at least one step of said cycle, and other means at each intersection continuously con nected tosame said condenser in at least one other step of said cycle to vary the charge on said condenser to said certain value, whereby said cyclic mechanism will operate through such cycle.

6. In a traific control system for a plurality of intersections of cross traific lanes with a common main lane having a right of way indicating means at each intersection and a controller thereat for operating the indicating means cyclically for according and interrupting right of way on the intersecting lanes, said controller including a cyclic step by step mechanism having means to change the right of way signal indication from one lane to another in stepping from one step to the next, a condenser, means when connected-to the condenser for charging said condenser, and electro-magnetic means adapted to be operated for advancing said cyclic mechanism from one step to the next, means for normally so operating said electro-magnetic means momentarily responsive to a certain charge on said condenser, a periodic impulse generating means at a central station for generating spaced electric impulses, a circuit from said generating means and common to all the controllers at all said intersections, for transmitting such impulses from said generating means to all said controllers, means in each controller responsive to said impulses for connecting in certain steps said charging means to said condenser during said impulses, means in each controller for interrupting such normal step by step advancing of said step by step mechanism from one step in its cycle, a second impulse generating means operated to generate impulses spaced at longer time periods than the first but in predetermined time relation thereto, a second circuit for transmitting the impulse from said second generating means to said controllers, and means in each controller responsive to said second impulse for operating directly said electro-magnetic means for advancing said cyclic mechanism independently of said charge responsive means from the step in which its advancing was interrupted, whereby the cycles of the several controllers are synchronized and completed.

7. In a traflic control system for a plurality of intersections of trafiic lanes having right of way indicating means at each intersection and a controller thereat for operating the indicating means cyclically for according and interrupting right of way on the intersecting lanes, the combination of a cyclic step by step mechanism having means to change the right of way signal indication from one lane to another in moving from one step to another, a condenser, electro-magnetic means adapted to be operated for advancing said cyclic mechanism from one step to the next, means to so operate said electro-magnetic means momentarily responsive to a charge of predetermined value on said condenser, means when connected to said condenser for varying the charge on said condenser progressively from an initial value to said predetermined value, a. periodic impulse generating means for generating spaced electric impulses, a circuit from said generating means and common to all the controllers at all said intersections for transmitting such impulses from said generating means to all said controllers, means in each controller responsive to said impulses for connecting in certain of said steps said charging means to said condenser during said impulses, other means connected continuously to said condenser in other of said steps to vary the charge on said condenser to said predetermined value in such other step, means in each controller for interrupting such normal step by step advancing of said step by step mechanism from one step in its cycle, a second impulse generating means operated to generate impulses spaced at longer time periods than the first but in predetermined time relation thereto, a second circuit for transmitting the impulse from said second generating means to said controllers, and means in each controller responsive to said second impulse for operating directly said electro-magnetic means for advancing said cycle mechanism independently of said charge responsive means from the step in which its advancing was interrupted, whereby the cycles of the several controllers are synchronized and completed.

THOMAS PHILIP PREIST. 

